Poliomyelitis

Question 1

Poliomyelitis

Answer 1

polio=grey
myelitis = marrow
-pathology caused by destruction of grey matter of CNS - paralysis

Question 2

Polio

Answer 2

-virus enters through mouth and multiplies in the intestine
-invades nervous system and can cause paralysis in a matter of hours
-initial symptoms: fever, fatigue, headache, V, stiffness in neck
-1 in 200 infections leads to irreversible paralysis
5-10% of these paralysed will die when breathing becomes infected
-mainly affects children under 5

Question 3

SALK vaccine 1955

Answer 3

Inactivated

-effective, killed

Question 4

SABIN vaccine 1962

Answer 4

• oral vaccine

- live attenuated

Question 5

Poliovirus particle structure

Answer 5

• enterovirus
• icosahedral
• atomic structure
• 60 copies of each of four capsid proteins

Question 6

REPLICATION

Answer 6

1. Receptor-mediated entry
2. Uncoating
3. Inhibition of cellular protein
   synthesis and translation (cap-
   binding protein)
4. Polyprotein synthesis
5. Co-translational processing
6. Protein-vesicle association
7. RNA-vesicle association
8. Negative strand synthesis
9. Positive strand synthesis
10. More translation
11. Capsid-RNA association
12. Packaging
13. Cell lysis and virus release

Question 7

CD155

Answer 7

poliovirus receptor PVR

-receptor mediated entry

Question 8

POLIO REPLICATION LOCATION

Answer 8

genome replication occurs in a membrane vesicle, not in the nucleus

Question 9

Polio pathogenesis

Answer 9

• Virus is transmitted faecal-orally
• Multiplies locally at initial sites (tonsils, Peyer’s patches)
or the lymph nodes that drain these sites.
• Virus shed in the throat and faeces
• Virus may enter CNS by peripheral or cranial nerve
axonal flow
• Viraemia leads to virus replication in secondary sites
(muscle predominantly, but also lymph nodes & brown
fat)
• Peripheral or cranial nerve retrograde axonal flow gives
virus access to CNS
• High levels of virus replication in CNS destroys motor neurones leading to paralysis (in ~0.5% infections).

Question 10

Poliovirus replication in the gut

Answer 10

is dependent on gut microflora

Question 11

IPV

Answer 11

inactivated polio vaccine -SALK

Question 12

OPV

Answer 12

oral polio vaccine -SABIN

-gives good secretory IgA antibody protection and lifelong protection

Question 13

Attenuation of poliovirus

Answer 13

• virus isolated
• grown in human cultured cells
• cultured virus used to infect monkey cells
• virus acquires many mutations
• no longer grows in human cells and may be good vaccine

Question 14

Killed -SALK

Answer 14

• effective
• no reversion

-no secretory IgA

Question 15

Live attenuated - SABIN

Answer 15

• lifelong immunity
• secretory immunity

-reversion

Question 16

Eradication of poliomyelitis

Answer 16

Possible because no animal vector or reservoir